ABSTRACT

INTRODUCTION

There are two main causes doing color researches interesting for aquaculture. First, the appearance of a food plays the important role not only at a customer’s choice of a product (Calvo, 1992), but it affects taste characteristics, influences the pleasantness and acceptability of foods (Clydesdale, 1993). Secondly, the physiological role of the compounds causing color, is important for organisms. One of the most widespread pigments of sea and freshwater organisms are carotenoids – lipophilic tetraterpenoid pigments, de novo synthesised only by plants and microorganisms and on food chains be received at higher trophic levels (Britton, 1983).

Carotenoids are widely used in aquaculture, mainly to obtain of natural coloring of salmon flesh, at rearing of Crustaceans (Meyers, 1994), and molluscs (Tsushima & Matsuno, 1998). A source of pigments can be microalgae, a processing waste of Crustacean, synthetic carotenoids identical to natural ones. Invertebrates are able to converse assimilated β-carotene to carotenoids necessary for them (for example astaxanthin for Crustaceans), but Salmonoids are deprived of such metabolism.

Carotenoids can occur free and associated with proteins. Formation of a carotenoprotein complex may lead to considerable bathochromic shift in an absorption spectrum and therefore these complexes often have purple, blue or green color, unlike yellow or orange color of free carotenoids (Britton, 1983). Color of shell is caused with crustacyanin in many Crustacean species. In ovaries a share of carotenoids can be associated with high-molecular protein - vitellin (Wallace et al., 1967). During vitellogenesis presence of this complex imparts bright color of ovaries (Meusy, Payen, 1988).

The major carotenoids of Crustacean species is astaxanthin, some authors proposed that it is a “semi-essential” nutrient for these animals. Its content is critical to a survival of larvae, sensibility of adult animals to stressful conditions, reproductive success etc. (Chien et al., 2003; Higuera-Ciapara et al., 2006). Sometimes alterations in carotenoid metabolism lead to change of usual appearances of cultivated animals.

CAROTENOIDS AS COLORANTS OF SALMONOID FLESH

However, in Crustacean aquaculture carotenoid pigments have mostly physiological function and they are not as important for color formation as in a case with salmon fish. It is well known, that pink coloring of a muscular tissue at salmon is caused first by the concentration of astaxanthin (in some cases of canthaxanthin). Unlike invertebrates, fish cannot synthesize astaxanthin from β-carotene, in their natural habitat major source of pigments for them is their feed, small crustaceans. At artificial rearing addition of astaxanthin (of astaxanthin containing components) to feed is considered more preferable, in comparison with canthaxanthin as former does not give undesirable increase in yellowness of a tissue (Screde & Storebakken, 1986). In case of uncontrollable growth of microalgae containing high quantity of β-carotene in ponds for cultivation, muscular tissue salmon can become yellow because of accumulation of this pigment that is unattractive to customers who prefer usual red color. In one’s turn, it leads to substantial losses for aquaculture farms.

vary greatly. In sea urchin gonads, except gametes (sexual cells), there is a considerable quantity of auxiliary cells which provide former with trophic and energy resources (Varaksina, 1980; Khotimchenko et al., 1993). At early stages of gametogenesis sexual tubules are mostly filled with the auxiliary cells containing yellow-orange globules due to presence of carotenoids (Varaksina, 1985, Jondeung and Czihak, 1983). In the process of growth, maturing and accumulation of gametes there is a carrying of nutrients (including carotenoids) from auxiliary cell into sexual ones. However, presence of carotenoids is detected only in female gametes (Lawrence, 2001).

CAROTENOIDS OF SEA URCHINS AND THEIR EFFECTS

ON ANIMAL HEALTH

Systematic study of the carotenoids in sea urchins, carried out by M. Tsushima and coworkers (Tsushima and Matsuno, 1990; Tsushima et al., 1993a), has shown that gonads, gut walls, tests and spines contain these pigments. Though the authors identified a significant number of minor pigments, the major carotenoids in gonads are β-echinenone, α-echinenone and β-carotene. Tsushima and Matsuno (1990) for the first time have separated fraction of echinenones in sea urchins and have identified of isomer of β-echinenone - α-echinenone. The only species at which the predominant carotenoids in gonads and gut walls were astaxanthin was Peronella japonica. It is not clear however, whether this species is capable to oxidize β-carotene to astaxantin, or it gets astaxantin from feed.

The metabolism of carotenoids in sea urchins has been studied for species Pseudocentrotus depressus (Tsushima et al., 1993b; Tsushima, 1995). Feeding experiments showed, that assimilated from feed β - and α-carotenes are oxidized to corresponding echinenones, the further transformation of β-echinenone into canthaxanthin and astaxanthin does not occur. The same authors have studied the importance of carotenoids, also vitamins A and Е for oogenesis and a survival of larvae of P. depressus (Tsushima et al., 1997). It was found, that the greatest number of larvae and the best survival have been observed for β- carotene and β-echinenone groups of animals. According to de Jong-Westman et al. (1995b), larvae of S. droebachiensis, rearing at laboratory conditions, the greatest sizes, highest survival rate and a metamorphosis were observed if parental individuals received feed containing β-carotene.

It has been established, that unlike Crustaceans and vertebrates sea urchins does not contain vitamin A (Tsushima et al., 1997). Later, it has been confirmed for Paracentrotus lividus Rodriguez-Bernaldo de Quirós et al. (2001).

In the many of the studies on sea urchin carotenoids, the geometrical configuration of echinenone has not been specified. Usually presence of a cis-isomer was considered as an artifact. However, for sea urchins, apparently, it is not true. For the first time occurrence of significant amounts of cis-isomer in P. lividus have been reported by de Nicola and Goodwin (1954). In gonads of Tripneustes gratila cis-echinenon was found as predominant isomer (Shina et al., 1978). Tsushima & Matsuno (1997) identified cis-isomer as 9′Z-β-echinenone in P. depressus. It was confirmed as major carotenoids in Paracentrotus lividus also (Symonds et al., 2007). Thus, cis-form of echinenone is dominant and widespread in sea urchins, but its function is not clear yet.